This invention relates to positioning systems, and more particularly to positioning systems useful in optical systems such as spectroanalytical systems of the absorption type.
Frequently, it is desirable to provide rapid, reliable and repeatable shifting of optical components such as radiation sources into and out of a precise analytical position.
In accordance with one aspect of the invention, there is provided a positioning mechanism for moving support structure between first and second predetermined positions. The support structure is mounted for movement relative to a reference member by a plurality of stabilizing coupling assemblies, and drive structure produces motion of the support structure relative to the reference structure between first and second stop structures that define the first and second predetermined positions, respectively. Interlock structure responds to the drive force generated by the drive structure and de-energizes the drive structure in response to the drive force applied to that support structure exceeding a predetermined threshold value.
In preferred embodiments, a plurality of groups of radiation sources are mounted at a sequence of levels or positions on the support structure and level selection structure includes stop structure which defines an analysis position corresponding to a particular group of radiation sources.
In a particular embodiment, the coupling assemblies provide stable support structure guidance and include counter-gravity biasing arrangements that minimize the load of the support structure on the drive structure.
In a particular embodiment, the drive structure includes a drive motor and a threaded drive shaft that are coupled together by a elongated flexible force transmitting drive member. An idler member is biased to apply tension to the force transmitting member. A controller energizes the drive motor in forward or reverse direction through a bridge circuit and concurrently releases a brake. The interlock structure responds to increased tension (of less than ten pounds) in the flexible force transmitting drive member and opens an interlock switch in the circuit to concurrently de-energize the drive motor and apply the brake to hold the drive shaft in fixed position.
In that embodiment, the positioning system is incorporated in a spectroanalytical system that includes an optical system with a bank of cassettes containing up to eight hollow cathode lamps in two arrays of four each in vertically spaced planes on a platform support structure. A selected array of hollow cathode lamps is accurately positioned by the positioning system in an analytical plane, and a particular hollow cathode lamp is selected by a galvanometer driven mirror system. Optically coupled to the hollow cathode lamp array is an analysis region for thermally exciting a sample material to be analyzed and a high-resolution monochromator with a galvanometer driven grating for line selection, a dual beam optical pathway, and a high sensitivity photomultiplier detector.
The galvanometer drives for wavelength and lamp selection are fast (a wavelength range of more than five hundred nanometers in less than one hundred milliseconds) and of high resolution (0.08 to two nanometers). The analysis system is like an inexpensive plasma spectrometer with extraordinary sensitivity and can be configured to determine large number of elements is a single unattended run with each element being determined at PPB levels.